1. Field of the Invention
The present invention relates to a sheet material information detection apparatus for detecting sheet material information by applying an external force to a sheet material, and more particularly, to a control in a case where there occurs abnormality with the sheet material entering a detection unit.
2. Description of the Related Art
In recent years, in sheet material processing apparatuses, typified by image forming apparatuses (such as Laser Beam Printer, copying machine, and ink jet printer), there is diversification of types of sheet materials to be processed. There is also diversification of users and use environment of the sheet material processing apparatus. Only with regard to the image forming apparatus, for the sheet materials of the diversified types, there is an increase in demand for higher quality (higher image quality, higher processing speed, and the like). On the other hand, with the diversification of sheet materials and diversification of processing contents, the number of items to be set by the user becomes enormous, thereby making it difficult to set an optimum processing condition. Therefore, a technique, in which various sensors are arranged in the sheet material processing apparatus to automatically identify sheet material information including a size, a thickness, and a quality of the sheet material, and automatically set an optimum processing condition, is put into practical use in some cases.
Japanese Patent Application Laid-Open No. 2005-024550 discloses a sheet material information detection apparatus having a structure in which an impact application member is allowed to impact a sheet material, and an impact through the sheet material is detected by an external force detection unit using a piezoelectric element. In this case, a voltage output of the piezoelectric element deformed by receiving the impact is detected to determine a peak value of the detected voltage output, thereby specifying a type of the sheet material. The piezoelectric element is sandwiched between an impact receiving member and a buffer member, and the impact received by the impact receiving member through the sheet material exerts a compression force on an entire surface of the piezoelectric element.
Japanese Patent Application Laid-Open No. 2004-038983 discloses a system which makes a database of various pieces of sheet material information, the database being shared by a plurality of printers. In this case, the sheet material information include texture, glossiness, ink absorbency, luminance, gross, color reflection, color depth, graininess, whiteness, humidity, heat loss, adhesiveness, and bonding property. When the sheet material is designated, a requisite piece of sheet material information is taken out from the database to a selected printer. Processing setting optimized based on the sheet material information is automatically set for the printer.
Japanese Patent Application Laid-Open No. H10-152245 discloses a sheet material information detection apparatus arranged in a transport path for a sheet material in an image forming apparatus. In this case, electrode terminals are brought into contact with upper and lower surfaces of the sheet material to measure resistivity and a moisture amount of the sheet material.
The sheet material information detection apparatus as disclosed in Japanese Patent Application Laid-Open No. 2005-024550 detects the sheet material by sandwiching a single passing sheet material in a thickness direction. Accordingly, when the folded sheet material or the stacked sheet materials enter therein, normal detection cannot be performed.
Further, a detection mechanism including a mechanical operation portion is precisely assembled by using lightweight components. Accordingly, there is a risk of the detection mechanism receiving deformation or damage when the sheet material impacts thereon at high speed or the stacked sheet materials are strongly caught therein.
Further, in the sheet material information detection apparatus as disclosed in Japanese Patent Application Laid-Open No. 2005-024550, the impact application member and the external force detection unit are arranged in positions which sandwich a transport height position of the sheet material so as to be opposed to each other, and a distance therebetween also serves as the transport path for the sheet material. Therefore, according to a state of the sheet material or transport conditions thereof, there may be a case where the folded sheet material clogs (so-called sheet clogging (also referred to as jam)) between the impact application member and the external force detection unit. In this case, the sheet material cannot easily be removed from an upstream side or from a downstream side. When the sheet material is forcedly drawn out, there is a risk in that not only the sheet material itself may be broken, but also a member coming into contact with the sheet material (including the sheet material information detection apparatus) may be broken, or damaged. There is a risk in that while the breakage is not caused, at least one of the impact application member and the external force detection unit is strained, thereby causing the impact application member and the external force detection unit to go out of alignment.
In particular, a high-speed image forming apparatus has a high transport speed for the sheet material. Therefore, when the sheet material clogs in the transport path, the folded sheet material exerts a substantial force on peripheral contact sections, so a risk of peripheral members being broken increases.
The conventional examples disclosed in Japanese Patent Application Laid-Open No. 2004-038983 and Japanese Patent Application Laid-Open No. H10-152245 include no countermeasure such as prevention of breakage in a case where there occurs abnormality such as the clogging of the sheet material.